# frozen_string_literal: true
# rubocop:disable Metrics/MethodLength
# rubocop:disable Metrics/LineLength
# rubocop:disable Metrics/ClassLength
# rubocop:disable Metrics/BlockLength
# rubocop:disable Style/Documentation

module Gitlab
  module BackgroundMigration
    class NormalizeLdapExternUidsRange
      class Identity < ActiveRecord::Base
        self.table_name = 'identities'
      end

      # Copied this class to make this migration resilient to future code changes.
      # And if the normalize behavior is changed in the future, it must be
      # accompanied by another migration.
      module Gitlab
        module LDAP
          class DN
            FormatError = Class.new(StandardError)
            MalformedError = Class.new(FormatError)
            UnsupportedError = Class.new(FormatError)

            def self.normalize_value(given_value)
              dummy_dn = "placeholder=#{given_value}"
              normalized_dn = new(*dummy_dn).to_normalized_s
              normalized_dn.sub(/\Aplaceholder=/, '')
            end

            ##
            # Initialize a DN, escaping as required. Pass in attributes in name/value
            # pairs. If there is a left over argument, it will be appended to the dn
            # without escaping (useful for a base string).
            #
            # Most uses of this class will be to escape a DN, rather than to parse it,
            # so storing the dn as an escaped String and parsing parts as required
            # with a state machine seems sensible.
            def initialize(*args)
              if args.length > 1
                initialize_array(args)
              else
                initialize_string(args[0])
              end
            end

            ##
            # Parse a DN into key value pairs using ASN from
            # http://tools.ietf.org/html/rfc2253 section 3.
            # rubocop:disable Metrics/AbcSize
            # rubocop:disable Metrics/CyclomaticComplexity
            # rubocop:disable Metrics/PerceivedComplexity
            def each_pair
              state = :key
              key = StringIO.new
              value = StringIO.new
              hex_buffer = ""

              @dn.each_char.with_index do |char, dn_index|
                case state
                when :key then
                  case char
                  when 'a'..'z', 'A'..'Z' then
                    state = :key_normal
                    key << char
                  when '0'..'9' then
                    state = :key_oid
                    key << char
                  when ' ' then state = :key
                  else raise(MalformedError, "Unrecognized first character of an RDN attribute type name \"#{char}\"")
                  end
                when :key_normal then
                  case char
                  when '=' then state = :value
                  when 'a'..'z', 'A'..'Z', '0'..'9', '-', ' ' then key << char
                  else raise(MalformedError, "Unrecognized RDN attribute type name character \"#{char}\"")
                  end
                when :key_oid then
                  case char
                  when '=' then state = :value
                  when '0'..'9', '.', ' ' then key << char
                  else raise(MalformedError, "Unrecognized RDN OID attribute type name character \"#{char}\"")
                  end
                when :value then
                  case char
                  when '\\' then state = :value_normal_escape
                  when '"' then state = :value_quoted
                  when ' ' then state = :value
                  when '#' then
                    state = :value_hexstring
                    value << char
                  when ',' then
                    state = :key
                    yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                    key = StringIO.new
                    value = StringIO.new
                  else
                    state = :value_normal
                    value << char
                  end
                when :value_normal then
                  case char
                  when '\\' then state = :value_normal_escape
                  when ',' then
                    state = :key
                    yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                    key = StringIO.new
                    value = StringIO.new
                  when '+' then raise(UnsupportedError, "Multivalued RDNs are not supported")
                  else value << char
                  end
                when :value_normal_escape then
                  case char
                  when '0'..'9', 'a'..'f', 'A'..'F' then
                    state = :value_normal_escape_hex
                    hex_buffer = char
                  else
                    state = :value_normal
                    value << char
                  end
                when :value_normal_escape_hex then
                  case char
                  when '0'..'9', 'a'..'f', 'A'..'F' then
                    state = :value_normal
                    value << "#{hex_buffer}#{char}".to_i(16).chr
                  else raise(MalformedError, "Invalid escaped hex code \"\\#{hex_buffer}#{char}\"")
                  end
                when :value_quoted then
                  case char
                  when '\\' then state = :value_quoted_escape
                  when '"' then state = :value_end
                  else value << char
                  end
                when :value_quoted_escape then
                  case char
                  when '0'..'9', 'a'..'f', 'A'..'F' then
                    state = :value_quoted_escape_hex
                    hex_buffer = char
                  else
                    state = :value_quoted
                    value << char
                  end
                when :value_quoted_escape_hex then
                  case char
                  when '0'..'9', 'a'..'f', 'A'..'F' then
                    state = :value_quoted
                    value << "#{hex_buffer}#{char}".to_i(16).chr
                  else raise(MalformedError, "Expected the second character of a hex pair inside a double quoted value, but got \"#{char}\"")
                  end
                when :value_hexstring then
                  case char
                  when '0'..'9', 'a'..'f', 'A'..'F' then
                    state = :value_hexstring_hex
                    value << char
                  when ' ' then state = :value_end
                  when ',' then
                    state = :key
                    yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                    key = StringIO.new
                    value = StringIO.new
                  else raise(MalformedError, "Expected the first character of a hex pair, but got \"#{char}\"")
                  end
                when :value_hexstring_hex then
                  case char
                  when '0'..'9', 'a'..'f', 'A'..'F' then
                    state = :value_hexstring
                    value << char
                  else raise(MalformedError, "Expected the second character of a hex pair, but got \"#{char}\"")
                  end
                when :value_end then
                  case char
                  when ' ' then state = :value_end
                  when ',' then
                    state = :key
                    yield key.string.strip, rstrip_except_escaped(value.string, dn_index)
                    key = StringIO.new
                    value = StringIO.new
                  else raise(MalformedError, "Expected the end of an attribute value, but got \"#{char}\"")
                  end
                else raise "Fell out of state machine"
                end
              end

              # Last pair
              raise(MalformedError, 'DN string ended unexpectedly') unless
                [:value, :value_normal, :value_hexstring, :value_end].include? state

              yield key.string.strip, rstrip_except_escaped(value.string, @dn.length)
            end

            def rstrip_except_escaped(str, dn_index)
              str_ends_with_whitespace = str.match(/\s\z/)

              if str_ends_with_whitespace
                dn_part_ends_with_escaped_whitespace = @dn[0, dn_index].match(/\\(\s+)\z/)

                if dn_part_ends_with_escaped_whitespace
                  dn_part_rwhitespace = dn_part_ends_with_escaped_whitespace[1]
                  num_chars_to_remove = dn_part_rwhitespace.length - 1
                  str = str[0, str.length - num_chars_to_remove]
                else
                  str.rstrip!
                end
              end

              str
            end

            ##
            # Returns the DN as an array in the form expected by the constructor.
            def to_a
              a = []
              self.each_pair { |key, value| a << key << value } unless @dn.empty?
              a
            end

            ##
            # Return the DN as an escaped string.
            def to_s
              @dn
            end

            ##
            # Return the DN as an escaped and normalized string.
            def to_normalized_s
              self.class.new(*to_a).to_s.downcase
            end

            # https://tools.ietf.org/html/rfc4514 section 2.4 lists these exceptions
            # for DN values. All of the following must be escaped in any normal string
            # using a single backslash ('\') as escape. The space character is left
            # out here because in a "normalized" string, spaces should only be escaped
            # if necessary (i.e. leading or trailing space).
            NORMAL_ESCAPES = [',', '+', '"', '\\', '<', '>', ';', '='].freeze

            # The following must be represented as escaped hex
            HEX_ESCAPES = {
              "\n" => '\0a',
              "\r" => '\0d'
            }.freeze

            # Compiled character class regexp using the keys from the above hash, and
            # checking for a space or # at the start, or space at the end, of the
            # string.
            ESCAPE_RE = Regexp.new("(^ |^#| $|[" +
                                   NORMAL_ESCAPES.map { |e| Regexp.escape(e) }.join +
                                   "])")

            HEX_ESCAPE_RE = Regexp.new("([" +
                                   HEX_ESCAPES.keys.map { |e| Regexp.escape(e) }.join +
                                   "])")

            ##
            # Escape a string for use in a DN value
            def self.escape(string)
              escaped = string.gsub(ESCAPE_RE) { |char| "\\" + char }
              escaped.gsub(HEX_ESCAPE_RE) { |char| HEX_ESCAPES[char] }
            end

            private

            def initialize_array(args)
              buffer = StringIO.new

              args.each_with_index do |arg, index|
                if index.even? # key
                  buffer << "," if index > 0
                  buffer << arg
                else # value
                  buffer << "="
                  buffer << self.class.escape(arg)
                end
              end

              @dn = buffer.string
            end

            def initialize_string(arg)
              @dn = arg.to_s
            end

            ##
            # Proxy all other requests to the string object, because a DN is mainly
            # used within the library as a string
            # rubocop:disable GitlabSecurity/PublicSend
            def method_missing(method, *args, &block)
              @dn.send(method, *args, &block)
            end

            ##
            # Redefined to be consistent with redefined `method_missing` behavior
            def respond_to?(sym, include_private = false)
              @dn.respond_to?(sym, include_private)
            end
          end
        end
      end

      def perform(start_id, end_id)
        return unless migrate?

        ldap_identities = Identity.where("provider like 'ldap%'").where(id: start_id..end_id)
        ldap_identities.each do |identity|
          begin
            identity.extern_uid = Gitlab::LDAP::DN.new(identity.extern_uid).to_normalized_s
            unless identity.save
              Rails.logger.info "Unable to normalize \"#{identity.extern_uid}\". Skipping."
            end
          rescue Gitlab::LDAP::DN::FormatError => e
            Rails.logger.info "Unable to normalize \"#{identity.extern_uid}\" due to \"#{e.message}\". Skipping."
          end
        end
      end

      def migrate?
        Identity.table_exists?
      end
    end
  end
end
